Resonator having counter rotating rigid parts

ABSTRACT

There is disclosed a resonator having rigid oscillating parts interconnected by a resilient web for inducing counterrotary movement of the rigid parts. The rigid parts are mounted to rotate about the nodal axis thereof. The nodal axis of each rigid part intersects the center of gravity of the part.

United States Patent Baker, Jr. 1 1 *Jan. 30, 1973 541 RESONATOR HAVINGCOUNTER 2,978,597 4 1961 Harris ..310/8 2 ROTATING RIGID PARTS 3,354,41311/1967 K 3,582,698 6/1971 Baker [75] Inventor: Hugh M. Baker, JL,Washington, 3 3 9 200 2 9 Kunnemunde D.C. 3,091,708 5/1963 Harris .1

. 3,308,313 3/1967 F [73] Assgneei 'f Cmpommm 1,781,513 11 1930 uiil teck Sliver Spring, 3,389,351 6 1968 Trzeba 3,281,725 /1966 Albsmeier 1Nome T gztfigg fi f l 3,146,415 8 1964 Albsmeieret a1. 1. y 3,376,5224/1968 Traub has 3,408,514 10/1968 Adamietz et a1. [22] Filed: Sept. 11,1970 2,469,951 5/1949 Cooley 2,939,971 6/1960 Holt ..310/ [21] Appl.No.: 71,394

FOREIGN PATENTS OR APPLICATIONS Related U.S. Application Data 43/183528/1968 Japan ..333/71 [63] Continuation of Ser. No. 565,430, July 15,1966.

' Primary Examiner-Herman Karl Saalbach [52] U.S. Cl. ..3l0/8.2, 84/409,84/457, Attorney-G, Turner Moller 331/116 M, 58/23 TF, 310/25, 333/72[51] Int. Cl. ..H0lv 7/00 [57] ABSTRACT [58] Fleld of Search.:....333/71, 72; There is disclosed a resonator having rigidOscillating 331/116 116 parts interconnected by a resilient web forinducing M; 73/505; 58/23 TF; 84/409 counterrotary movement of the rigidparts. The rigid 5 parts are mounted to rotate about the nodal axis [56]References Cited thereof. The nodal axis of each rigid part intersectsUNlTED STATES PATENTS the center of gravity of the part.

3,453,464 7/1969 Baker ..310/36 15 Claims, 8 Drawing Figures PATENTEDJAN30 ms SHEET 10F 2 INVENTOR. HUG/1 M BAKER Jr PATENTEDJAHBO 19153,714,475 sum 2 or 2 PW INVENTOR.

HUGH M. BAKER Jr RESONATOR HAVING COUNTER ROTATING RIGID PARTS Thisapplication is a continuation of application Ser. No. 565,430, filedJuly 15, 1961.

This invention relates to resonators, filters, and more particularly toelectromechanical type resonators and filters with piezoelectric,magnetostrictive and electromagnetic drive.

At frequencies below KC, electromechanical filters and resonators aregenerally chosen over capacitance and resistance networks or capacitanceand inductance networks since they offer the best temperature stability,frequency selectivity, small size and low cost combination.

While there are many forms of electromechanical resonators and filters,the ones most often selected for frequencies below 20 KC are tuningforks, some form of a simply supported loaded beam, and the cantileveredloaded beam.

Each of these devices has certain design, manufacturing or performancedeficiencies. A common objectionable characteristic is reaction felt inthe supporting members. Consequently, unless great care is taken toisolate one reasonating device from another, there will be objectionableinteraction between them particularly when they are functioning as afrequency selective filter.

Another objectionable characteristic common to all of these devices,especially if they are loaded with high relative mass to obtain lowfrequency with high selectivity, is that they are affected by theattitude of their mounting or support because of gravitational effects.A tuning fork, for example, resonates at one frequency when mountedhorizontally and another frequency when mounted vertically.

When the desired resonant frequency is very low, the physical size ofall three forms of resonators becomes a significant factor relative tothe frequency selectivity. The flexing members, being very large, aredampened heavily by the surrounding medium such as air, atmosphere orthe like. Thus, it is common practice to evacuate the surrounding mediumfrom the container in which the structure is mounted in order to improveits frequency selectivity. The simply supported beam as well ascantilevered beam type of resonator have the further disadvantage ofcomparatively poor frequency selectivity in part due to dampingintroduced by a nonrigid base.

It is known by those versed in the art of electromechanical resonatorsthat frequency selectivity is generally improved if the flexible portionof the resonator is made stiffer and a load is added to maintain a givenfrequency. In general, the frequency selectivity of the resonator isimproved by a factor related to the square root of the product of thestiffness and the loading.

In the case of the simply supported beam and the v cantilevered beamtype of resonator, this is offset by a to obtain a combination ofthermo-elastic properties and compensating thermo-expansion properties.

Because of the physical form of a tuning fork type of resonator, greatcare must be taken to avoid disturbing the compensating effects of thesetwo properties when bringing the tuning fork to the desired frequencyonce it is assembled.

In any form of mechanical resonator, the resonant frequency thereof canbe adjusted only by changing the physical parameters of the structuredthe resonator. Because such adjustments are generally awkward andtime-consuming, they are permanent or semi-permanent in nature. Thereare many applications wherein it would be advantageous to produce acontrolled temporary shift of the resonant frequency with ease andrapidity. It would be particularly advantageous if this shift could beaccomplished by electrical means.

In order to overcome the disadvantages as stated above and to acquirethe unforeseen, unobvious and desired results of the instant inventiveconcept as will be more fully described and disclosed hereinafter, it isan object of my invention to construct a mechanical resonator which maybe piezoelectrically electromagnetically and magnetostrictively drivenwhile not being affected by the position or mounting attitude thereofwith the resonator having virtually no reaction impressed on themounting base and therefore having minimal tendency for one resonator toadversely affect an adjacent resonator.

It is also of my invention to provide a mechanical resonator which issimple and inexpensive to design and construct with respect to frequencyselectivity and thermal-frequency stability, and to achieve a highdegree of frequency selectivity in a small size without need forevacuating the surrounding media from the container in which theresonator may be disposed.

Another object of this invention is to construct an electromechanicalresonator which is substantially totally free of the effects of gravityand acceleration on the resonant frequency.

It is a further object of this invention to construct anelectromechanical resonator assembly which may be semi-permanentlyadjusted over some range of resonant frequencies with ease and withoutcutting away or adding material to the loaded or flexing portions of theassembly.

It is a further object of this invention to provide an assembly by whichthe resonant frequency of any electromechanical resonator may betemporarily shifted a controlled amount with ease and rapidity viaelectrical means.

It is also a further object of this invention to provide anelectromechanical resonator whose basic configuration is in the generalform of the letter I-I.

Other objects and important features of the invention would be apparentfrom a study of the specification following taken with the drawing,which together show, illustrate, describe and disclose preferredembodiments or modifications of the invention and it is now consideredto be the best mode of practicing the principles thereof. Still otherembodiments or modifications may be suggested to those having thebenefit of the teachings herein, and such other embodiments ormodifications are intended to be reserved especially as they fall withinthe scope and spirit of the subjoined claims.

IN THE DRAWING FIG. 1 shows a perspective view of one embodiment of amechanical type resonator having the improvements of this inventionincorporated therewith;

FIG. 2 is a plan view of the resonator as illustrated in FIG. 1;

FIG. 3 is a diagramatic illustration of the relative position of certainvarious parts of the resonator illustrated in FIG. 1 taken during acycle of oscillation;

FIG. 4 is a plan view similar to FIG. 2 of the drawing but showinganother embodiment thereof in which a plurality of resonators similar tothose illustrated in FIGS. 1 and 2 may be cascaded to improve thefrequency selectivity;

FIG. 5 is a perspective view of the resonator shown in FIG. 1 butillustrating a structural arrangement as well as a method ofelectrically tuning the resonator by employing a plurality of additionaltransducers;

FIG. 6 is a plan view of the resonator illustrated in FIG. 1 showinganother embodiment of the structural arrangement and method ofelectrically tuning the resonator;

FIG. 7 shows a perspective view of a typical tuning fork illustratingthe structural arrangement and the method for electrically tuning samewhich is similar to that as illustrated in FIG. 5, and

FIG. 8 is a plan view of the tuning fork shown in FIG. 7 butillustrating the embodiment of the structural arrangement and method forelectrically tuning same as being similar to that as illustrated in FIG.6.

Attention is now directed to FIGS. 1 and 2 of the drawing wherein thereis illustrated a novel resonator structure 10 which will be describedand disclosed herein as being employed as a filter and in such capacity,the resonator 10 will possess certain highly desired, unobvious andunforeseen characteristics and will be explained in more detailhereinafter. It is to be expressly noted that the resonator 10 has abasic configuration which may be considered as being substantially inthe form of an H with the resonator 10 being defined by an elongatefirst part 12 that is relatively bodily rigid having a longitudinalextent D and an elongate second part 14 which is also relatively bodilyrigid and which is substantially coextensive with the first part 12having similar longitudinal extent D.

The first 12 and the second 14 parts of the resonator structure 10 aredisposed in parallel relationship relative to each other and are spacedapart a distance d.

The resonator structure 10 is further provided with an elongate thirdpart which extends between and is connected to an intermediate portion18 of each of the first 12 and the second 14 parts of the resonatorstructure 10.

For the sake of illustration only, the first l2 and the second 14 partsof the resonator structure 10 have been shown as being of rectangularconfiguration in cross section with the third part 16 having arelatively large surface area. However, it to be understood that othershapes and configurations may be employed with regard to the first 12,second 14, and third 16 parts of the resonator structure 10 withoutdeparting from the spirit of the inventive concept which is beingdescribed and disclosed.

There are, however, certain physical characteristics of the parts l2, l4and 16 which are believed to be of importance, such as: the mass of eachof the parts l2 and 14 should be substantially greater than the mass ofthe third part 16, the longitudinal extent D of the parts 12 and 14should be substantially greater than the distance d of the spacetherebetween, the material from which the first 12 and the second 14parts are made should have a relatively low coefficient of expansionwith the third part being formed of material having an isoelasticproperty, the intermediate portions 18 of the first 12 and second 14parts as well as the third part 16 should be located in a plane that iscommon with the nodal axes 20 of the first 12 and the second 14 parts ofthe resonator structure 10 being defined respectively by the innersection of a longitudinal plane that is disposed along the one half thewidth W and a transverse plane which is disposed along the one halflongitudinal extent D of the parts 12 and 14.

The resonator structure 10 is further provided with transducers 22 whichin the form as illustrated in FIG. 1 of the drawing is a piezoelectricmaterial. However, other transducers may be employed in the form ofelectromagnetostrictive or electromagnetic without departing from theinstant inventive concept.

The transducers 22 are secured to the third part 16 of the resonatorstructurelO, in any suitable manner and as illustrated, the pair oftransducers 22 is employed with one transducer 22 being disposed on eachof the opposed surfaces of the third part 16 of the resonator structure10. Depending on the type of electrical circuitry to be employed, thenumber of transducers 22 may vary and the inventive concept asillustrated is an example of a three terminal type filter arrangement.If a two terminal type filter is to be employed, it is only necessary tohave a single transducer 22 secured to the third part 16 of theresonator structure 10.

In the three terminal circuitry as illustrated, electrical signals areapplied to one of the transducers through a wire 24 and the signalsgenerated on the other transducer 22 disposed on the opposed side of thebodily flexible third part 16 is taken off through another wire 26. Byreason of the fact that the flexible third part 16 is disposed betweenthe transducers 22, the flexible third part 16 in effect creates anelectrical connection therebetween and the signals created therein aretaken off through a wire 28 making the electrical network an effectivethree terminal device.

If the electrical signal is applied to the flexible third part 16 of theresonator structure 10 through the wire 24 and the transducers 22associated therewith the flexible third part 16 will assume a positionas illustrated in FIG. 3 by the reference character A during one halfcycle and by reason of the connection of the third part 16 to each ofthe first 12 and second 14 parts of the resonator structure 10, therelatively rigid nonflexing first l2 and second 14 parts will assume aposition as illustrated by the reference character B. During the secondone half cycle of the electrical signal, the flexible third part 16 willassume a position illustrated by the reference character E in FIG. 3 ofthe drawing which will position the nonflexing bodily rigid first 12 andsecond 14 parts of the resonator structure 10 in positions asillustrated by the reference character F. In FIG. 3 of the drawing thenormal or relaxed positions of the first 12, second 14 and third 16parts of the resonator structure are illustrated in solid lines with therelative positions thereof during the one half cycle being shown bydotted lines and referred to with the third part 16 being illustrated bythe reference character A and the first 12 and second 14 parts beingillustrated by the reference character B with the relative positionsthereof during the second half cycle of the electrical signal beingshown with the third part 16 designated by the reference character E andthe first 12 and second 14 parts illustrated by the reference characterF. It will thus be apparent that the counterrotation between the parts12, 14 is substantially coextensive in time in the sense that the parts12, 14 begin rotation at substantially the same time and end atsubstantially the same time. Chronocoextensive is used to describe thisrelationship.

The result of passing the electrical signal to the bodily flexible thirdpart 16 of the resonator structure is that a counter rotationaloscillation is created in the first l2 and second 14 parts of theresonator structure 10 occurs about the respective nodal axes 20 and byreason of a rotational or pivotal connection 30, to be described in moredetail hereinafter that is provided between the resonator structure 10and a support structure 32 there is no reaction to the rockingoscillatory motion of the bodily rigid non-flexing first 12 and second14 parts since the parts 12 and 14 are, in effect, counterbalancing eachother about the pivotal connections along the nodal axes 20.

Having thus balanced all of the various parts or portions of theresonator structure 10 about the rotational or pivotal connections 30which are common with the respective nodal axes 20 there is no effectivegravitational forces or influences operating on the resonator structure10 against the resonant frequency which may be created thereby. In otherwords, in dealing with the low frequencies with which we are currentlyinterested, and with the relative properties and characteristics beingin existence that relate to the first 12, second 14 and third 16 parts,such as the relative masses etc., and by reason of the non-flexingrelatively bodily rigid first 12 and second 14 parts beingcounterbalanced about the rotational or pivotal connections, there isvirtually no effect created by any gravitational forces or influences onthe resonant frequency of the resonator structure 10 and further, thecharacteristics and relative relationship of the parts as disclosed anddescribed creates a condition in which acceleration also has virtuallyno effect on the resonant frequency of the resonator structure 10.

In the resonator structure 10, as herein described and disclosed, theresultant resonant frequency is determined by the relative stiffness ofthe bodily flexible third part 16 and the mass as well as the moment ofinertia about the pivotal connections 30 of the bodily rigid non-flexingfirst 12 and second 14 parts and in the preferred embodiment ormodification of the resonator structure 10 the bodily flexible thirdpart 16 is preferably formed of a material which has the property ofisoelasticity, that is, a material whose elastic properties are leastaffected by temperature changes such as a material which may be ahomogenus steel alloy of 30 percent nickel and 10 percent chromium asdescribed and disclosed in U.S. Pat. No. 1,763,853 with the bodily rigidfirst l2 and second 14 parts being of a material having a lowcoefficient of expansion such as Invar or certain glass compounds.

None of the moving parts of the resonator structure 10 are comparativelylarge for a given resonant frequency and further because the total ofdistance of travel of any moving part of the resonant structure 10 issimilar, the damping effects of the surrounding atmosphere are minimal.If it is desirable to recuce the damping effects of the surroundingatmosphere even further the non-flexing bodily rigid first 12 and second14 parts may be made of circular cross section wherein the modal axes 20would extend through the longitudinal center lines thereof at a locationwhich is halfway of the longitudinal extent with the nodal axes beingnormal to the longitudinal axes thereof.

By reason of the description and disclosure made herein, it is believedobvious on passing the electrical signal through the resonator structure10 that a resultant resonantfrequency will be created and it is undercertain conditions highly desirable to be able to vary the resultantresonant frequency and in order to so vary the resultant frequency thereis provided structure 34 which will effectively semi-permanentlyefficiently and readily enable the resonant frequency of the resonatorstructure 10 to be varied.

As illustrated in FIG. 1 of the drawing, the structure 34 comprises agenerally longitudinally extending bore 36 that passes along thelongitudinal axis of each of the first l2 and second 14 parts in whichthere is longitudinally spaced a plurality of plug-like members 38 withthe plug-like members 38 being retained within the respective bore 36 bysuitable securements such as a press or friction set as well as screwthreads or the like. The relative position of each of the plug-likemembers 38 from the respective nodal axes 20 will, in effect, vary theresonant frequency of the resonator structure 10 and by reason of themass of the plug-like members 38 the moment of inertia of the first l2and second 14 parts may be varied by reason of the disposition of theplug-like members 38 relative to the respective nodal axes 20. It is tobe understood that the plug-like members 38 should be of the samemassand position the same distance from the respective nodal axes 20 inorder to maintain the balance of the resonator structure 10.

It is to be understood that an arrangement similar to the plug-likemembers 38 and the bore 36 may be conveniently employed on resonatorssuch as tuning forks, cantilevered beams, some forms of simple supportedbeams and other similar mechanical resonators to effectively vary theresonant frequency thereof by varying the moment of inertia in a mannersimilar to that as described and disclosed herein with regard to thefirst l2 and second 14 parts of the resonator structure 10.

The support structure 32 may comprise as illustrated a base portion 40from which there projects a plurality of bracket-like members 42 withthe bracket like-members 42 being disposed in pairs, one pair beingadjacent the first l2 and another pair adjacent the second 14 parts ofthe resonator structure 10 with the first 12 and second 14 parts thereofbeing intermediate the respective pair of the bracket-like members 42.

A suitable pivotal pin type connection 44 extends between the associatedpair of bracket-like members 42 and passes through the respective nodalaxes 20 and the associated first l2 and second 14 parts of the resonatorstructure 10 and the pivotal pin type connectors 44 divide therotational or pivotal connection 30 for supporting the resonatorstructure 10 with the first l2 and the second 14 parts thereof being inthe counterbalanced condition.

Attention is now directed to FIG. 4 of the drawing wherein there isillustrated another embodiment or modification of the inventive conceptwherein it is desired to obtain a better selection of resonant frequencyand in this embodiment or modification there is provided a plurality ofresonator structures 10 which are disposed in cascaded relationshiprelative to each other.

It is to be noted that the pivotal pin type connectors 44 are common tothe adjacent resonator structures 10 and thus enable the motion of oneof the resonator structures 10 to be coupled to the next adjacentresonator structure 10. It is to'be understood that the disposition of aplurality of resonator structures 10 in cascading relationship relativeto each other should not be limited to two and by extending orincreasing the number of resonator structures 10 which may be employedthere occurs a corresponding improvement in the resonant frequencyselectivity. Further, the resonator structures 10 which may be disposedin the cascaded relationship as illustrated may be electrically coupledwith no-mechanical coupling, electrically and mechanically coupled ormechanically coupled in order to obtain a specific frequency selectivitycharacteristic.

Attention is now directed to FIGS. 5 through 8 of the drawing whereinthere is illustrated and shown certain embodiments and modifications ofan apparatus and method for changing or varying the existing resonantfrequency of a resonator and as illustrated in FIG. 5 of the drawing,the resonator 10 is illustrated and like characters of reference arerelied upon for the purpose of identification which should correspond tothe character references as shown in FIGS. 1 and 2. p

The resonator structure 10, as previously described and disclosed, isdriven through the external circuit which is connected by the wire 24that is attached to the one transducer 22 which is illustrated as apiezoelectric wafer with the resonator structure 10 thus effectivelyhaving a resultant resonant frequency which, for reasons previouslystated, may be desirable to vary or change.

Apparatus 46 is provided for varying or changing the resultant resonantfrequency of the resonator structure 10 and the apparatus 46 comprisesat least one and preferably a pair of additional transducers 48 which,as illustrated, are in the form of piezoelectric wafers with theadditional transducers 48 being secured to bodily flexible third part 16of the resonator structure 10 and suitable wiring 50 is provided tocreate a circuit that comprises a potentiometer 52 that is in serieswith a battery or source of electrical energy 54 so that a DC voltagewhich may be varied is applied to the additional transducers 48.

As illustrated in FIG. 7, a similar apparatus 46 is employed to aconventional type of tuning fork 56 having a plurality of tines 58 towhich there is secured the additional transducers 48 which are providedwith wiring 50 that creates a circuit that includes the potentiometer 52and the source of electrical energy 54, all in a manner similar to thecircuitry of FIG. 5.

Since in any mechanical resonating device there is a relationshipbetween the resultant resonant frequency and the stiffness of theflexible portion of the resonant structure the resultant resonantfrequency may be shifted, changed, varied or altered by the relativestiffness of the flexible member or members as the case may be. ln theresonant structure 10 and 56, as illustrated in FIGS. 5 and 7 of thedrawing, the additional transducers 48 employed in the apparatus 46 formpart of the respective bodily flexible portions or members, that is thethird part 16 and the tines 58 and contribute to shifting, changingvarying or altering the relative stiffness thereof. As the voltage ofthe circuitry of the apparatus 46 which is supplied from the source ofelectrical energy 54 through the potentiometer 52 and the wiring 50 isapplied across the additional transducers 48, the additional transducers48 will stretch or contract according to the polarity and magnitude ofthe applied voltage as varied by the potentiometer 52.

By attaching or securing the additional transducers 48 to the bodilyflexible portions or members 16 and 58 of the resonator structures 10 or46, as the case may be, so that the additional transducers 48 aredisposed on opposite surfaces of the associated bodily flexible part ormember the additional transducers 48 will tend to stretch or contract,in the same direction in response to a given applied voltage andaccordingly, increase or decrease, as the case may be the relativestiffness of the part 16 or member 58 in response to the variance of thevoltage from the source of electrical energy 54 as opposite polaritiesthereof is applied.

The result of employing the apparatus 46 as a method for altering,shifting, varying or changing the resultant resonant frequency of aresonator structure is that the resultant resonant frequency may bealtered, shifted, varied to correspond to the magnitude or polarity ofthe voltage which may be applied from the source of electrical energy 54which passes through the additional transducers 48.

While the apparatus 46 has been illustrated in FIGS. 5 and 7 of thedrawing as having a component part thereof piezoelectric wafers whichdefine the transducers 48, it may be desired that the additionaltransducers 48 take the form of an electromagnet 60 which, asillustrated in FIGS. 6 and 8 of the drawing may be employed with theapparatus 46 to alter, vary, change, shift or modify the resultantresonant frequency of resonator structures 10 and tuning forks 56.

As illustrated in FIG. 6 of the drawing, the electromagnet 60 isdisposed between the first l2 and the second 14 bodily rigid part of theresonator structure 10 with the electromagnetic field thereof beingcontrolled by a coil 62 which is connected through the wiring 50 to asource of electrical energy 54 and a potentiometer 52.

As current from the source electrical energy 54 is increased by thepotentiometer 52 to the coil 62, such an increase in the current willthus increase the influence of the magnetic field which will in turnbring a strain or bias to the end portions of the first 12 and thesecond 14 parts of the resonator structure 10 and such strain or biaswill influence and thus vary, change, modify and effectively control therelatively flexibility of the third part 16 and thus alter the stiffnessthereof. Accordingly, the resultant resonant frequency of the resonatorstructure 10 may be altered, influenced, varied and changed inaccordance with the current flow to the electromagnetic 60.

Similarly and as illustrated in FIG. 8 of the drawing, theelectromagnetic 60 may be placed between the tine members 58 of aresonator structure which may be in the form of a tuning fork 56 and asthe current flow to the coil 62 of the apparatus 46 will influence theflexibility of the tine members 58 and thus vary, change, modify andcontrol the resultant resonant frequency thereof.

The variation of the electromagnetic field of the apparatus 46 asillustrated in FIG. 8 through varying the current from the source ofelectrical energy 54 by the potentiometer 52 is reflected as a change inthe stress on the tine members 58 which thus changes the relativestiffness thereof and as the stiffness is altered, there is acorresponding change in the resonant frequency of the tuning fork 56.While the invention has been shown, illustrated, described and disclosedin terms of certain embodiment or modifications which it has assumed inpractice, the scope of the invention should not be deemed to be limitedby the precise embodiment or modification has herein shown, illustrated,described or disclosed and such other embodiments or modificationsintended to be reserved especially as they fall within the scope of theclaims here appended.

I claim:

1. A resonator comprising first and second parts rigid at a resonantfrequency of the resonator;

means supporting the first part to enable the same to rotate about thenodal axis thereof, means supporting the second part to enable the sameto rotate about the nodal axis thereof, the nodal axes substantiallyintersecting the centers of gravity of the respective first and secondparts;

means for providing a resilient connection between the first and secondparts for inducing counter rotary movement of the first and second partsupon a movement of one of the parts, the resilient means comprising athird part connected to the first and second parts and flexible at aresonant frequency of the resonator; and v means for moving at least oneof the parts.

2. The resonator of claim 1 wherein the nodal axes define a plane.

3. The resonator of claim 2 wherein the first and second parts aresubstantially parallel.

4. The resonator of claim 1 wherein the third part is independent of thesupporting means.

5. The resonator of claim 1 wherein the resilient means comprises meansfor transmitting rotary movement of the first part into counterrotarymovement of the second part.

6. The resonator of claim 1 wherein the resilient means comprises meansfor transmitting rotary movement of the first part into substantiallysimultaneous counter rotation of the second part.

7. The resonator of claim 1 wherein the moving means comprises anelectromechanical transducer disposed on the third part.

8. The resonator of claim 1 wherein the third part comprises a planersection and the moving means comprises an electromechanical transduceron surfaces of he planar section which are in opposed relation to eachother.

9. The resonator as set forth in claim 1 wherein the first and secondparts are formed of material having a relatively low coefficient ofexpansion, and the third part is formed of material having isoelasticproperties.

10. The resonator as set forth in claim 1 wherein the mass of the firstand second parts are each substantially greater than the mass of thethird part.

11. The resonator as set forth in claim 1 wherein the length of thefirst and second parts are each substantially greater than the spacetherebetween.

12. The resonator as set forth in claim 1 wherein the mass moment ofinertia of the first part is substantially equal to the mass moment ofinertia of the second part.

13. The resonator of claim 12 wherein the connection between the thirdpart and each of the first and second parts produces equal momentson thefirst and second parts upon rotation thereof.

14. The resonator of claim 1 wherein the nodal axes are spaced apart.

15. The resonator of claim 1 further comprising means for adjusting theresonant frequency of the resonator including means for changing therelative stiffness of the third part.

1. A resonator comprising first and second parts rigid at a resonantfrequency of the resonator; means supporting the first part to enablethe same to rotate about the nodal axis thereof, means supporting thesecond part to enable the same to rotate about the nodal axis thereof,the nodal axes substantially intersecting the centers of gravity of therespective first and second parts; means for providing a resilientconnection between the first and second parts for inducing counterrotary movement of the first and second parts upon a movement of one ofthe parts, the resilient means comprising a third part connected to thefirst and second parts and flexible at a resonant frequency of theresonator; and means for moving at least one of the parts.
 1. Aresonator comprising first and second parts rigid at a resonantfrequency of the resonator; means supporting the first part to enablethe same to rotate about the nodal axis thereof, means supporting thesecond part to enable the same to rotate about the nodal axis thereof,the nodal axes substantially intersecting the centers of gravity of therespective first and second parts; means for providing a resilientconnection between the first and second parts for inducing counterrotary movement of the first and second parts upon a movement of one ofthe parts, the resilient means comprising a third part connected to thefirst and second parts and flexible at a resonant frequency of theresonator; and means for moving at least one of the parts.
 2. Theresonator of claim 1 wherein the nodal axes define a plane.
 3. Theresonator of claim 2 wherein the first and second parts aresubstantially parallel.
 4. The resonator of claim 1 wherein the thirdpart is independent of the supporting means.
 5. The resonator of claim 1wherein the resilient means comprises means for transmitting rotarymovement of the first part into counterrotary movement of the secondpart.
 6. The resonator of claim 1 wherein the resilient means comprisesmeans for transmitting rotary movement of the first part intosubstantially simultaneous counter rotation of the second part.
 7. Theresonator of claim 1 wherein the moving means comprises anelectromechanical transducer disposed on the third part.
 8. Theresonator of claim 1 wherein the third part comprises a planer sectionand the moving means comprises an electromechanical transducer onsurfaces of the planar section which are in opposed relation to eachother.
 9. The resonator as set forth in claim 1 wherein the first andsecond parts are formed of material having a relatively low coefficientof expansion, and the third part is formed of material having isoelasticproperties.
 10. The resonator as set forth in claim 1 wherein the massof the first and second parts are each substantially greater than themass of the third part.
 11. The resonator as set forth in claim 1wherein the length of the first and second parts are each substantiallygrEater than the space therebetween.
 12. The resonator as set forth inclaim 1 wherein the mass moment of inertia of the first part issubstantially equal to the mass moment of inertia of the second part.13. The resonator of claim 12 wherein the connection between the thirdpart and each of the first and second parts produces equal moments onthe first and second parts upon rotation thereof.
 14. The resonator ofclaim 1 wherein the nodal axes are spaced apart.